Since you're doing AFF in the US, check out the USPA progression card here and look at the freefall skills. It seems like you've already got most of what you can work on the tunnel down (arch & turn). Working off of that, you can experiment with different body positions and learn to fly more with your legs/core instead of your arms. You can also try out some flips & barrel rolls (with a spotter!). Talk to the tunnel instructors as well, let them know that you intend to do AFF and they should be able to work up some exercises for you.

I personally like to work on fall rate control & RW when I'm in the tunnel because I fall like a brick but I like doing RW and I'd like to get my coach rating eventually (can't fall out on a student!).

Chances are your weight distribution will be somewhat different when you first skydive, since you'll be wearing a parachute rig (and a big, heavy student rig at that!) This will probably put your centre of gravity further forward but you may not really notice it. More and more people are wearing dummy rigs in the tunnel now to better approximate actual freefall.

The really big thing about the tunnel is having the walls as a reference. When you're learning this is a good thing because it helps you develop the muscle memory that keeps you on heading and in place, although you may find the lack of reference a little disconcerting when you get into the air. Experienced skydivers often find themselves bouncing off the walls the first time they fly in a tunnel - partly because it is a little different, and partly because they never realised how much they move around in the sky.

Some things will be completely new, of course - exits, and all that inconvenient stuff involving the use of parachutes - there's no way (yet!) to simulate those properly in the tunnel.

And aside from all the physical limitations, never underestimate the effect on your brain of actually jumping out of an aeroplane for the first time.

MikeJD - Thanks for the reassurance that what i'm doing will ultimately be useful, although slightly different.

Based on that I may have a search around for a dummy rig to wear in tunnel to get as close as i can to reality.

Your last paragraph "aside from all the physical limitations, never underestimate the effect on your brain of actually jumping out of an aeroplane for the first time" really made me think as yes, I have seen the all the you tube videos's where the student does absolutely nothing and forgets he has to pull, or spins out upside down etc. It's that bit I'm hoping to avoid

Lastly I'm pleasantly surprised at just how helpful people are here and I must admit, I paused before posting the thread as these to everyone else are such basic questions and I thought I might get shot down but that's not been the case.

Canopy... ~~This is the phase of the jump where most fatalities and serious injuries occur. (Serious injury or death in freefall above pull altitude is rare). ~~A bad freefall and a good canopy flight = "good jump" ~~A good freefall and a bad canopy flight = "ambulance ride"

Have you tried talking to the tunnel instructors? Chances are they could put you in touch with someone who would do pre AFF training there. Or venture south - Bodyflight near Bedford definitely does pre-AFF training and can lend dummy rigs.

You will be taught the exit in your AFF program. (The details of that exit will vary based on aircraft used and specific technique preferred by your DZ). Don't sweat it. A nice stable arch with chin up is what you are taught in the tunnel... and it will be very valuable during your exit.

The transition from horizontal wind to vertical wind is known as "The Hill". It lasts a few seconds (~5). Many skydivers find that flying on the hill is one of the best parts of freefall.